1. Field of the Invention
The invention pertains to the art of characterizing the phase and amplitude transfer functions of radio frequency (RF) amplifiers.
2. Art Background
In an ideal radio frequency (RF) amplifier which has its gain set by an external bias level, the amplifier gain would be a linear, monotonic function of the bias level, and there would be no phase shift in the amplified signal over the range of bias and gain settings. Unfortunately, ideal amplifiers are hard to find. In many radio frequency (RF) applications, it is desirable or necessary to characterize the gain and phase transfer functions of RF amplifiers with respect to frequency and bias, often as a part of a manufacturing process or device test.
Traditionally, this analysis is performed using a two-port network analyzer. The network analyzer provides a reference input signal to the device under test (DUT) through a first port. The network analyzer, through a second port, captures the output of the DUT, and by comparing this captured output signal to the reference input signal, calculates the change in amplitude, or gain, of the amplifier, and the phase shift. This measurement process may be repeated over variations in parameters such as frequency, input amplitude, amplifier bias, and the like, to characterize the performance of the DUT.
In modern wireless devices, such as wireless communications devices, it may be difficult or impossible to make two port measurements of the output amplifier stage of the device. It may be difficult to perform a two port test measuring amplitude and phase response of the amplifier, for example during device test.
What is needed is a way to characterize amplitude and phase transfer functions of RF amplifiers using single port measurements.